Polymeric materials are used in numerous applications in modern technology. In order to be useful, the polymers are molded, extruded or formed into various shapes and shaped articles. For the polymer to take the shape of the formed article, the physical state of the polymer must be sufficiently pliable so that it may be readily worked into the desired shape. This pliability or flow is usually achieved by melting the polymer and forcing the polymer into the desired shape with a specific tool such as an extruder, an injection mold, compression mold, blow mold and the like.
During this forming or shaping process, the polymer is subjected to various extremes of temperature, pressure and the like as well as other unknown factors. When a single polymer is employed, the shaped article generally only has a minimum of molding problems, usually due to the specific properties of the polymer. However when an admixture of two or more different polymers is formed into a shaped article, problems beyond those caused by the specific properties of each individual polymer can occur. Unless the polymers are completely soluble in each other at the temperature the shaped article is formed, or to which it is cooled, partitioning of the nonsoluble polymers into domains can occur. There may be domains of admixed polymers having a different weight percent composition of component polymers than the remainder of the admixed polymers in the shaped article. Such differences in composition occur with some frequency at the surface of the shaped article. Although the phenomonon is not completely understood it appears that molecular weight and melt viscosity are contributing factors to the partitioning of constituent polymers of blends to the surface of a shaped article during its formation under elevated temperature. A shaped article which has this laminar structure or "laminate" is oftentimes unaffected by its presence as measured by its property profile.
However, many times the laminate does not adhere well to the remainder of the shaped article and in time undesirable changes occur. These changes, generally referred to as "delamination", include but are not limited to the flaking, peeling, or cracking of the surface skin after a period of time. When delamination occurs the appearance of the shaped article obviously suffers. Appearance is of great significance in articles such as housings and painted pieces. Moreover the delamination exposes the interior portion of the shaped article to the presence of various chemicals and environmental effects which it may not withstand. It is quite apparent that significant delamination can render a shaped article unfit for its intended use. This delamination can be observed in shaped articles as small as 1/8 inch pellets formed by a knife cutting an extrudate.